Nearly all roadways are posted with physical speed limit signs. The speed limits may be set according to a wide variety of rules and by different entities. Countries or states may set speed limits for interstates or major highways, and municipalities such as cities and towns may set speed limits for smaller roads and streets. The speed limits may be selected under rules based on the curvature or lane width of the road. The speed limits may be selected under rules based on the proximity to urban or rural areas. Other considerations such as school zones, bridges, or pedestrian crossings may impact the selection of speed limits. Because of these variable situations, it may not be possible to reliably identify the speed limit of a road from the placement of the road or shape of the road on the map. Instead, posted speed limits are detected in order to identify speed limits of roads on the map. Other indicia or road postings may be similarly inconsistent.
Once speed limits or other indicia or road postings are detected, the data may be associated with the appropriate road link. Because of variances in sign locations, this may not be a straightforward process. Challenges remain in reliably associating correct sign values with their respective road links.